Compositions of dibromomalonamide and their use as biocides

ABSTRACT

A biocidal composition comprising 2,2-dibromomalonamide and an isothiazolinone-based biocide, and its use for the control of microorganisms in aqueous and water-containing systems.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/246,184, filed Sep. 28, 2009, which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to biocidal compositions and methods of their use for the control of microorganisms in aqueous and water-containing systems. The compositions comprise 2,2-dibromomalonamide and an isothiazolinone based biocide.

BACKGROUND OF THE INVENTION

Water systems provide fertile breeding grounds for algae, bacteria, viruses, and fungi some of which can be pathogenic. Microbial contamination can create a variety of problems, including aesthetic unpleasantries such as slimy green water, serious health risks such as fungal, bacterial, or viral infections, and mechanical problems including plugging, corrosion of equipment, and reduction of heat transfer.

Biocides are commonly used to disinfect and control the growth of microorganisms in aqueous and water containing systems. However, not all biocides are effective against a wide range of microorganisms and/or temperatures, and some are incompatible with other chemical treatment additives. In addition, some biocides do not provide microbial control over long enough time periods.

While some of these shortcomings can be overcome through use of larger amounts of the biocide, this option creates its own problems, including increased cost, increased waste, and increased likelihood that the biocide will interfere with the desirable properties of the treated medium. In addition, even with use of larger amounts of the biocide, many commercial biocidal compounds cannot provide effective control due to weak activity against certain types of microorganisms or resistance of the microorganisms to those compounds.

It would be a significant advance in the art to provide biocide compositions for treatment of water systems that yield one or more of the following advantages: increased efficacy at lower concentrations, compatibility with physical conditions and other additives in the treated medium, effectiveness against a broad spectrum of microorganisms, and/or ability to provide both short term and long term control of microorganisms.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the invention provides a biocidal composition. The composition is useful for controlling microorganisms in aqueous or water containing systems. The composition comprises: 2,2-dibromomalonamide and an isothiazolinone-based biocide of the formula I:

wherein R, R¹, and Y are as defined below.

In a second aspect, the invention provides a method for controlling microorganisms in aqueous or water containing systems. The method comprises treating the system with an effective amount of a biocidal composition as described herein.

DETAILED DESCRIPTION OF THE INVENTION

As noted above, the invention provides a biocidal composition and methods of using it in the control of microorganisms. The composition comprises: 2,2-dibromomalonamide and an isothiazolinone-based biocide of the formula I as shown below. It has surprisingly been discovered that combinations of 2,2-dibromomalonamide and an isothiazolinone-based biocide as described herein, at certain weight ratios, are synergistic when used for microorganism control in aqueous or water containing media. That is, the combined materials result in improved biocidal properties than would otherwise be expected based on their individual performance. The synergy permits reduced amounts of the materials to be used to achieve the desired biocidal performance, thus reducing problems caused by growth of microorganisms in industrial process waters while potentially reducing environmental impact and materials cost.

For the purposes of this specification, the meaning of “microorganism” includes, but is not limited to, bacteria, fungi, algae, and viruses. The words “control” and “controlling” should be broadly construed to include within their meaning, and without being limited thereto, inhibiting the growth or propagation of microorganisms, killing microorganisms, disinfection, and/or preservation.

The term “2,2-dibromomalonamide” refers to a compound represented by the following chemical formula:

The isothiazolinone-based biocide of the composition of the invention is of the formula I:

wherein R and R¹ are independently hydrogen, halogen or C₁-C₄ alkyl, or R and R¹ together with the carbons to which they are attached from a C₄-C₇ cycloalkyl ring or an aryl group; and

Y is H, C₁-C₁₂ alkyl, C₃-C₇ cycloalkyl, aryl or aralkyl.

In some embodiments of the invention, R in formula I is H, or Cl. In some embodiments, R¹ is H or Cl. In some embodiments, R and R¹, together with the carbons to which they are attached, form phenyl or cyclopentyl.

In some embodiments of the invention, Y in formula I is H, CH₃, CH₂CH₃, or n-octyl.

In some embodiments, the isothiazolinone based biocide is: 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 4,5-dichloro-2-n-octylisothiazolin-3-one, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, 4,5-dichloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, N-methyl-1,2-benzisothiazolin-3-one, or N-butyl-1,2-benzisothiazolin-3-one.

In some embodiments, the isothiazolinone based biocide is: 5-chloro-2-methyl-4-isothiazolin-3-one (“CMIT”), 2-methyl-4-isothiazolin-3-one (“MIT”), 2-n-octyl-4-isothiazolin-3-one (“OIT”), 1,2-benzisothiazolin-3-one (“BIT”), 4,5-dichloro-2-n-octylisothiazolin-3-one (“DCOIT”), or a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, N-methyl-1,2-benzisothiazolin-3-one (“MBIT”), or N-butyl-1,2-benzisothiazolin-3-one (“BBIT”).

More than one isothiazolinone compound can be combined for use in the present invention; in such cases, ratios and concentrations are calculated using the total weight of all isothiazolinone compounds present.

Isothiazolinones for use in the invention are commercially available and/or can be readily prepared by those skilled in the art using well known techniques (see e.g., U.S. Pat. No. 5,312,827). 2,2-Dibromomalonamide is commercially available. In some embodiments, it is desirable to formulate the isothiazolinone containing compositions of the invention in solutions containing water or organic solvent or mixtures thereof together with nitrate or nitrite stabilizers to prevent decomposition of the isothiazolinone (see U.S. Pat. No. 3,870,795). In some embodiments, the stabilizer is magnesium nitrate.

In some embodiments of the invention, the weight ratio of 2,2-dibromomalonamide to isothiazolinone-based biocide is between about 100:1 and about 1:400.

In some embodiments, the weight ratio of 2,2-dibromomalonamide to isothiazolinone-based biocide is between about 70:1 and about 1:350.

In some embodiments, the weight ratio of 2,2-dibromomalonamide to isothiazolinone-based biocide is between about 32:1 and about 1:320.

In some embodiments, the isothiazolinone-based biocide is 5-chloro-2-methyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 5-chloro-2-methyl-4-isothiazolin-3-one is from about 100:1 to about 1:20, alternatively from about 70:1 to about 1:10, alternatively from about 40:1 to about 1:5, or alternatively from about 32:1 to about 1:2.

In some embodiments, the isothiazolinone-based biocide is 2-methyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 2-methyl-4-isothiazolin-3-one is from about 20:1 to about 1:20, alternatively from about 10:1 to about 1:10, or alternatively from about 4:1 to about 1:4.

In some embodiments, the isothiazolinone-based biocide is 4,5-dichloro-2-n-octylisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 4,5-dichloro-2-n-octylisothiazolin-3-one is from about 20:1 to about 1:20, alternatively from about 10:1 to about 1:20, or alternatively from about 4:1 to about 1:16.

In some embodiments, the isothiazolinone-based biocide is 1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 1,2-benzisothiazolin-3-one is from about about 20:1 to about 1:20, alternatively from about 10:1 to about 1:10, alternatively from about 1:1 to about 1:5, or alternatively from about 1:1.6 to about 1:5.

In some embodiments, the isothiazolinone-based biocide is 2-n-octyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 2-n-octyl-4-isothiazolin-3-one is from about about 20:1 to about 1:350, alternatively from about 1:1 to about 1:320, alternatively from about 1:2 to about 1:320, or alternatively from about 1:2.5 to about 1:320.

In some embodiments, the isothiazolinone-based biocide is N-methyl-1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the N-methyl-1,2-benzisothiazolin-3-one is from about about 20:1 to about 1:280, alternatively from about 1:1 to about 1:256.

In some embodiments, the isothiazolinone-based biocide is N-butyl-1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the N-butyl-1,2-benzisothiazolin-3-one is from about about 20:1 to about 1:20, alternatively from about 10:1 to about 1:10, alternatively from about 1:1 to about 1:8, or alternatively from about 1:2 to about 1:8.

The composition of the invention is useful for controlling microorganisms in a variety of aqueous and water containing systems. Examples of such systems include, but are not limited to, paints and coatings, aqueous emulsions, latexes, adhesives, inks, pigment dispersions, household and industrial cleaners, detergents, dish detergents, mineral slurries polymer emulsions, caulks and adhesives, tape joint compounds, disinfectants, sanitizers, metalworking fluids, construction products, personal care products, textile fluids such as spin finishes, industrial process water (e.g. oilfield water, pulp and paper water, cooling water, and air washers), oilfield functional fluids such as drilling muds and fracturing fluids, fuels, air washers, wastewater, ballast water, filtration systems, and swimming pool and spa water. Preferred aqueous systems are metal working fluids, personal care, household and industrial cleaners, industrial process water, and paints and coatings. Particularly preferred are industrial process water, paints and coatings, metal working fluids, and textile fluids such as spin finishes.

A person of ordinary skill in the art can readily determine, without undue experimentation, the effective amount of the composition that should be used in any particular application to provide microorganism control. By way of illustration, a suitable actives concentration (total for both 2,2-dibromomalonamide and isothiazolinone-based biocide) is typically at least about 1 ppm, alternatively at least about 3 ppm, alternatively at least about 7 ppm, alternatively at least about 10 ppm, or alternatively at least about 100 ppm based on the total weight of the aqueous or water containing system. In some embodiments, a suitable upper limit for the actives concentration is about 1000 ppm, alternatively about 500 ppm, alternatively about 100 ppm, alternatively about 50 ppm, alternatively about 30 ppm, alternatively about 15 ppm, alternatively about 10 ppm, or alternatively about 7 ppm, based on the total weight of the aqueous or water containing system.

The components of the composition can be added to the aqueous or water containing system separately, or preblended prior to addition. A person of ordinary skill in the art can easily determine the appropriate method of addition. The composition can be used in the system with other additives such as, but not limited to, surfactants, ionic/nonionic polymers and scale and corrosion inhibitors, oxygen scavengers, and/or additional biocides.

The following examples are illustrative of the invention but are not intended to limit its scope. Unless otherwise indicated, the ratios, percentages, parts, and the like used herein are by weight.

EXAMPLES

Growth Inhibition Assay. The growth inhibition assay used in the examples measures inhibition of growth (or lack thereof) of a microbial consortium Inhibition of growth can be the result of killing of the cells (so no growth occurs), killing of a significant portion of the populations of cells so that regrowth requires a prolonged time, or inhibition of growth without killing (stasis). Regardless of the mechanism of action, the impact of a biocide (or combination of biocides) can be measured over time on the basis of an increase in the size of the community.

The assay measures the efficacy of one or more biocides at preventing growth of a consortium of bacteria in a dilute mineral salts medium. The medium contains (in mg/l) the following components: FeCl₃.6H₂O (1); CaCl₂.2H₂O (10); MgSO₄.7H₂O (22.5); (NH₄)₂SO₄ (40); KH₂PO₄ (10); K₂HPO₄ (25.5); Yeast Extract (10); and glucose (100). After all components are added to deionized water, the pH of the medium is adjusted to 7.5.

Following filter sterilization, aliquots are dispensed in 100 ul quantities to sterile microtiter plate wells. Dilutions of 2,2-dibromomalonamide (“DBMAL”) and/or “Biocide B” are then added to the microtiter plate. After preparing the combinations of actives as illustrated below, each well is inoculated with 100 μl of a cell suspension containing ca. 1×10⁶ cells per milliliter of a mixture of Pseudomonas aeruginosa, Klebsiella pneumoniae, Staphylococcus aureus, and Bacillus subtilis. The final total volume of medium in each well is 300 μl. Once prepared as described herein, the concentration of each active ranges from 25 ppm to 0.19 ppm as illustrated in Table 1. The resulting matrix allows testing of eight concentrations of each active and 64 combinations of actives in the ratios (of actives).

TABLE 1 Template for microtiter plate-based synergy assay showing concentrations of each active. Ratios are based on weight (ppm) of each active. DBMAL (ppm) 25.000 12.500 6.250 3.13 1.563 0.781 0.391 0.19 Biocide B 25.000 1:1 1:2 1:4 1:8 1:16 1:32 1:64 1:128 (ppm) 12.500 2:1 1 1:2 1:4 1:8 1:16 1:32 1:64 6.250 4:1 2:1 1 1:2 1:4 1:8 1:16 1:32 3.13 8:1 4:1 2:1 1 1:2 1:4 1:8 1:16 1.563 16:1  8:1 4:1 2:1 1 1:2 1:4 1:8 0.781 32:1  16:1  8:1 4:1 2:1 1 1:2 1:4 0.391 64:1  32:1  16:1  8:1 4:1 2:1 1 1:2 0.19 128:1  64:1  32:1  16:1  8:1 4:1 2:1 1:1 Controls (not shown) contain the medium with no biocide added.

Immediately after the microtiter plates are prepared, the optical density (OD) readings for each well is measured at 580 nm and the plates are then incubated at 37° C. for 24 hr. After the incubation period, the plates are gently agitated before OD₅₈₀ values are collected. The OD₅₈₀ values at T₀ are subtracted from T₂₄ values to determine the total amount of growth (or lack thereof) that occurs. These values are used to calculate the percent inhibition of growth caused by the presence of each biocide and each of the 64 combinations. A 90% inhibition of growth is used as a threshold for calculating synergy index (SI) values with the following equation:

Synergy Index=M _(DBMAL) /C _(DBMAL) +M _(B) /C _(B)

where

-   -   C_(DBMAL): Concentration of DBMAL required to inhibit ˜90% of         bacterial growth when used alone     -   C_(B): Concentration of biocide (B) required to inhibit ˜90% of         bacterial growth when used alone.     -   M_(DBMAL): Concentration of DBMAL required to inhibit ˜90% of         bacterial growth when used in combination with biocide (B).     -   M_(B): Concentration of biocide (B) required to inhibit ˜90% of         bacterial growth when used in combination with DBMAL         The SI values are interpreted as follows:     -   SI<1: Synergistic combination     -   SI=1: Additive combination     -   SI>1: Antagonistic combination

In the Examples below, the amounts of biocides in the solution are measured in mg per liter of solution (mg/l). Since solution densities are approximately 1.00, the mg/l measurement corresponds to weight ppm. Both units may therefore be used interchangeably in the Examples.

Example 1 DBMAL and CMIT

Table 2 shows the assay results for DBMAL, 5-chloro-2-methyl-4-isothiazolin-3-one (“CMIT”), and combinations. In the assay, the minimum concentration of DBMAL in which growth of the consortium is at least 90% less than controls (e.g., I₉₀ value) is 12.5 mg/l. The I₉₀ value for CMIT is 0.78 mg/l. However, several combinations of the actives are inhibitory below their respective I₉₀ values. For example, a combination of 0.19 mg/l DBMAL and 0.38 mg/l CMIT results in 97% inhibition of growth of the microbial consortium.

TABLE 2 Percent inhibition of growth in a species-defined microbial consortium by DBMAL and CMIT alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (OD) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and CMIT in DBMAL growth CMIT of DBMAL Untreated Concn. by Concn. growth Concn. CMIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by CMIT (mg/l) 25.0 12.5 6.25 3.13 1.56 0.78 0.39 0.19 0 25.0 100 25.0 98 25.0 98 98 96 97 99 100 99 100 0 12.5 98 12.5 96 12.5 95 98 98 98 99 99 100 100 3 6.25 0 6.25 97 6.25 96 97 95 98 100 100 99 93 4 3.13 23 3.13 98 3.13 98 98 97 100 100 100 100 99 0 1.56 15 1.56 96 1.56 97 99 98 98 98 99 99 92 2 0.78 13 0.78 97 0.78 98 98 97 98 100 99 92 35 0 0.39 11 0.39 10 0.39 98 99 100 99 100 80 91 0 0 0.19 5 0.19 19 0.19 96 97 97 97 99 99 97 2

Table 3 shows concentrations of DBMAL and CMIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 3 DBMAL Concn. CMIT Concn. Ratio Synergy (mg/l) (mg/l) (DBMAL to CMIT Index (SI) 3.13 0.39 8:1 0.75 1.56 0.39 4:1 0.62 0.78 0.39 2:1 0.56 0.39 0.39 1:1 0.53 0.19 0.39 1:2 0.51 6.25 0.19 32:1  0.75 3.13 0.19 16:1  0.5 1.56 0.19 8:1 0.37

Example 2 DBMAL and MIT

Table 4 shows the assay results for DBMAL, 2-methyl-4-isothiazolin-3-one (“MIT”), and combinations thereof. The I₉₀ values for MIT and DBMAL were 25 mg/l and 12.5 mg/l, respectively. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 4 Percent inhibition of growth in a species-defined microbial consortium by MIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and MIT in DBMAL growth MIT of DBMAL Untreated Concn. by Concn. growth Concn. MIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by MIT (mg/l) 25.0 12.5 6.25 3.13 1.56 0.78 0.39 0.19 13 25.0 100 25.0 96 25.0 98 98 98 99 98 99 98 96 0 12.5 100 12.5 38 12.5 98 98 98 98 98 100 99 100 0 6.25 23 6.25 16 6.25 98 99 97 97 97 0 0 0 1 3.13 0 3.13 6 3.13 98 99 98 21 0 0 0 0 2 1.56 1 1.56 6 1.56 96 39 13 1 0 0 0 0 0 0.78 2 0.78 0 0.78 91 36 6 1 0 0 0 0 0 0.39 6 0.39 0 0.39 96 37 7 0 0 0 0 1 0 0.19 0 0.19 0 0.19 98 23 24 0 0 9 7 0

Table 5 shows concentrations of DBMAL and MIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 5 DBMAL Concn. MIT Concn. Ratio Synergy (mg/l) (mg/l) (DBMAL to MIT) Index (SI) 6.25 6.25 0.75 1:2 6.25 3.13 0.625 2:1 6.25 1.56 0.56 4:1 3.13 12.5 0.75 1:4 3.13 6.25 0.5 1:2

Example 3 DBMAL and DCOIT

Table 6 shows the assay results for DBMAL, 4,5-dichloro-2-n-octylisothiazolin-3-one (“DCOIT”), and combinations. The I₉₀ values for DCOIT and DBMAL were 6.25 mg/l and 12.5 mg/l, respectively. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 6 Percent inhibition of growth in a species-defined microbial consortium by DCOIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % % Inhibition Inhibition Inhibition of growth of of Combinations of DBMAL and DCOIT in DBMAL growth DCOIT growth DBMAL Untreated Concn. by Concn. by Concn. DCOIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) DCOIT (mg/l) 25.0 12.5 6.25 3.13 1.563 0.781 0.391 0.19 12 25.0 100 25.0 97 25.0 100 100 98 98 99 99 99 99 11 12.5 100 12.5 99 12.5 99 99 98 99 99 100 100 99 11 6.25 28 6.25 99 6.25 100 99 98 99 99 26 0 0 12 3.13 11 3.13 37 3.13 100 99 98 98 96 0 0 0 0 1.56 0 1.56 41 1.56 99 99 100 99 27 0 0 0 0 0.78 6 0.78 26 0.78 100 100 99 99 0 4 7 12 0 0.39 0 0.39 0 0.39 100 100 100 100 7 30 20 7 0 0.19 0 0.19 0 0.19 100 100 100 96 5 30 0 0

Table 7 shows concentrations of DBMAL and DCOIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 7 Synergy DBMAL Concn DCOIT Concn. Ratio Index (mg/l) (mg/l) (DBMAL to DCOIT) (SI) 3.13 3.13 1:1 0.75 1.56 3.13 1:2 0.63 0.78 3.13 1:4 0.56 0.39 3.13 1:8 0.53 0.19 3.13  1:16 0.52 6.25 1.56 4:1 0.75 3.13 1.56 2:1 0.5

Example 4 DBMAL and BIT

Table 8 shows the assay results for DBMAL, 1,2-benzisothiazolin-3-one (“BIT”), and combinations. The I₉₀ value for BIT is 15.63 mg/l and the I₉₀ value for DBMAL is 12.5 mg/l. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 8 Percent inhibition of growth in a species-defined microbial consortium by BIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and BIT in DBMAL growth BIT of DBMAL Untreated Concn. by Concn. growth Concn. BIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by BIT (mg/l) 250.0 125.0 62.5 31.25 15.63 7.81 3.91 1.95 1 25.0 99 250.0 97 25.0 99 99 97 98 99 99 99 99 0 12.5 100 125.0 98 12.5 99 99 98 100 99 100 99 99 4 6.25 45 62.5 98 6.25 98 100 100 100 99 98 98 97 1 3.13 8 31.25 99 3.13 98 100 100 100 100 100 60 0 0 1.56 0 15.63 96 1.56 99 98 100 100 100 97 52 0 6 0.78 1 7.81 46 0.78 99 100 100 100 96 37 10 0 7 0.39 3 3.91 17 0.39 98 98 99 98 64 30 0 0 0 0.19 0 1.95 0 0.19 98 99 96 98 61 30 0 0

Table 9 shows concentrations of DBMAL and BIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 9 DBMAL Concn. BIT Concn. Ratio Synergy Index (mg/l) (mg/l) (DBMAL to BIT) (SI) 3.13 7.81 1:2.5 0.75 1.56 7.81 1:5   0.62 6.25 3.91 1:1.6 0.75 6.25 1.95 1:3.2 0.62

Example 5 DBMAL and OIT

Table 10 shows the assay results for DBMAL, 2-n-octyl-4-isothiazolin-3-one (“OIT”), and combinations. The I₉₀ values for OIT and DBMAL were 125 mg/l and 12.5 mg/l, respectively. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 10 Percent inhibition of growth in a species-defined microbial consortium by OIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and OIT in DBMAL growth OIT of DBMAL Untreated Concn. by Concn. growth Concn. OIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by OIT (mg/l) 500.0 250.0 125.0 62.5 31.25 15.63 7.81 3.91 8 25.0 100 500.0 100 25.0 100 100 100 100 100 100 100 100 6 12.5 100 250.0 100 12.5 100 100 100 100 100 100 100 100 10 6.25 44 125.0 100 6.25 100 100 100 100 100 100 60 0 0 3.13 0 62.5 64 3.13 100 100 100 100 100 1 0 0 0 1.56 1 31.25 43 1.56 100 100 100 100 90 0 0 0 0 0.78 0 15.63 24 0.78 100 100 100 100 40 0 0 0 0 0.39 3 7.81 7 0.39 100 100 100 100 30 1 0 0 0 0.19 0 3.91 0 0.19 100 100 100 100 0 0 0 0

Table 11 shows concentrations of DBMAL and OIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 11 DBMAL Concn. OIT Concn. Ratio Synergy Index (mg/l) (mg/l) (DBMAL to OIT) (SI) 3.13 62.5 1:20 0.75 1.56 62.5 1:40 0.63 0.78 62.5 1:80 0.56 0.39 62.5 1:160 0.53 0.20 62.5 1:320 0.52 6.25 31.25 1:5 0.75 3.13 31.25 1:10 0.50 1.56 31.25 1:20 0.38 6.25 15.63 1:2.5 0.63

Example 6 DBMAL and MBIT

Table 12 shows the assay results for DBMAL, N-methyl-1,2-benzisothiazolin-3-one (“MBIT”), and combinations. The I₉₀ values for MBIT and DBMAL were 100.0 mg/l and 12.5 mg/l, respectively. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 12 Percent inhibition of growth in a species-defined microbial consortium by MBIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and MBIT in DBMAL growth MBIT of DBMAL Untreated Concn. by Concn. growth Concn. MBIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by MBIT (mg/l) 100.0 50.0 25.0 12.5 6.25 3.13 1.56 0.78 2 25.0 100 100.0 100 25.0 100 93 99 95 84 98 85 98 5 12.5 100 50.0 67 12.5 100 94 91 91 91 100 90 88 0 6.25 44 25.0 23 6.25 100 97 94 91 98 56 55 0 15 3.13 0 12.5 53 3.13 100 98 95 92 45 41 10 0 4 1.56 1 6.25 26 1.56 100 100 93 92 22 0 3 0 0 0.78 0 3.13 0 0.78 100 100 94 92 35 15 0 0 4 0.39 3 1.56 13 0.39 100 100 100 81 24 28 0 0 7 0.19 0 0.78 16 0.19 100 100 91 64 12 28 0 0

Table 13 shows concentrations of DBMAL and MBIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 13 DBMAL Concn. MBIT Concn. Ratio Synergy Index (mg/l) (mg/l) (DBMAL to MBIT) (SI) 3.13 50 1:16 0.75 1.56 50 1:32 0.63 0.78 50 1:64 0.56 0.39 50 1:128 0.53 0.20 50 1:256 0.52 6.25 25 1:4 0.75 3.13 25 1:8 0.50 1.56 25 1:16 0.38 0.78 25 1:32 0.31 0.39 25 1:64 0.28 0.20 25 1:128 0.27 6.25 12.5 1:2 0.63 3.13 12.5 1:4 0.38 1.56 12.5 1:8 0.25 0.78 12.5 1:16 0.19 6.25 6.25 1:1 0.56

Example 7 DBMAL and BBIT

Table 14 shows the assay results for DBMAL, N-butyl-1,2-benzisothiazolin-3-one (“BBIT”), and combinations. The I₉₀ values for BBIT and DBMAL were 50.0 mg/l and 12.5 mg/l, respectively. Several combinations of the actives are inhibitory below their respective I₉₀ values.

TABLE 14 Percent inhibition of growth in a species-defined microbial consortium by BBIT and DBMAL alone and combinations of these actives after a 24-hour incubation period. Numbers represent percent inhibition of growth as measured by optical density measurements (580 nm) at time = 24 hours compared with time = 0 values. Single Actives (mg/l) % % Inhibition Inhibition % of growth of Inhibition Combinations of DBMAL and BBIT in DBMAL growth BBIT of DBMAL Untreated Concn. by Concn. growth Concn. BBIT Concn. (mg/l) Control (mg/l) DBMAL (mg/l) by BBIT (mg/l) 50.0 25.0 12.5 6.25 3.13 1.56 0.78 0.39 4 25.0 100 50.0 100 25.0 100 100 93 97 89 99 89 92 7 12.5 93 25.0 49 12.5 100 100 95 99 91 93 93 93 9 6.25 34 12.5 24 6.25 100 100 95 62 14 0 0 0 6 3.13 0 6.25 32 3.13 100 100 50 31 10 0 0 4 0 1.56 0 3.13 0 1.56 100 76 23 8 0 0 6 0 0 0.78 0 1.56 1 0.78 100 51 0 0 0 0 0 0 12 0.39 3 0.78 0 0.39 99 39 3 0 0 0 0 0 0 0.19 0 0.39 7 0.19 100 74 7 0 0 2 0 0

Table 15 shows concentrations of DBMAL and BBIT found to be synergistic. The ratios are based on concentrations of the actives.

TABLE 15 DBMAL Concn. BBIT Concn. Ratio Synergy Index (mg/l) (mg/l) (DBMAL to BBIT) (SI) 3.13 25 1:8 0.75 6.25 12.5 1:2 0.75

While the invention has been described above according to its preferred embodiments, it can be modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using the general principles disclosed herein. Further, the application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the following claims. 

1. A biocidal composition comprising: 2,2-dibromomalonamide and an isothiazolinone-based biocide of the formula I:

wherein R and R¹ are independently hydrogen, halogen or C₁-C₄ alkyl, or R and R¹ together with the carbons to which they are attached from a C₄-C₇ cycloalkyl ring or an aryl group; and Y is H, C₁-C₁₂ alkyl, C₃-C₇ cycloalkyl, aryl or aralkyl.
 2. A composition according to claim 1 wherein the weight ratio of 2,2-dibromomalonamide to the isothiazolinone-based biocide of formula I is between about 100:1 and about 1:400.
 3. A composition according to claim 1 wherein the isothiazolinone-based biocide of the formula I is selected from the group consisting of: 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 4,5-dichloro-2-n-octylisothiazolin-3-one, a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, 4,5-dichloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, N-methyl-1,2-benzisothiazolin-3-one, or N-butyl-1,2-benzisothiazolin-3-one and mixtures of two or more thereof.
 4. A composition according to claim 1 wherein the isothiazolinone-based biocide of formula I is 5-chloro-2-methyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 5-chloro-2-methyl-4-isothiazolin-3-one is from about 32:1 to about 1:2.
 5. A composition according to claim 1 wherein the isothiazolinone-based biocide is 2-methyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 2-methyl-4-isothiazolin-3-one is from about 4:1 to about 1:4.
 6. A composition according to claim 1 wherein the isothiazolinone-based biocide is 4,5-dichloro-2-n-octylisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 4,5-dichloro-2-n-octylisothiazolin-3-one is from about 4:1 to about 1:16.
 7. A composition according to claim 1 wherein the isothiazolinone-based biocide is 1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 1,2-benzisothiazolin-3-one is from about about 1:1 to about 1:5.
 8. A composition according to claim 1 wherein the isothiazolinone-based biocide is 2-n-octyl-4-isothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the 2-n-octyl-4-isothiazolin-3-one is from about about 1:2 to about 1:320.
 9. A composition according to claim 1 wherein the isothiazolinone-based biocide is N-methyl-1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the N-methyl-1,2-benzisothiazolin-3-one is from about about 1:1 to about 1:256.
 10. A composition according to claim 1 wherein the isothiazolinone-based biocide is N-butyl-1,2-benzisothiazolin-3-one and the weight ratio of 2,2-dibromomalonamide to the N-butyl-1,2-benzisothiazolin-3-one is from about about 1:2 to about 1:8.
 11. A composition according to claim 1 which is: paint, coating, aqueous emulsion, latex, adhesive, ink, pigment dispersion, household or industrial cleaner, detergent, dish detergent, mineral slurry polymer emulsion, caulk, adhesive, tape joint compound, disinfectant, sanitizer, metalworking fluid, construction product, personal care product, textile fluid, spin finish, industrial process water, oilfield functional fluid, fuel, air washer, wastewater, ballast water, filtration systems, swimming pool water or spa water.
 12. A method for controlling microorganism growth in an aqueous or water-containing system, the method comprising treating the aqueous or water-containing system with an effective amount of a composition according to claim
 1. 13. A method according to claim 12 wherein the aqueous or water-containing system is paint, coating, aqueous emulsion, latex, adhesive, ink, pigment dispersion, household or industrial cleaner, detergent, dish detergent, mineral slurry polymer emulsion, caulk, adhesive, tape joint compound, disinfectant, sanitizer, metalworking fluid, construction product, personal care product, textile fluid, spin finish, industrial process water, oilfield functional fluid, fuel, air washer, wastewater, ballast water, filtration system, swimming pool water, or spa water. 